Positive electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using the same

ABSTRACT

[Object] Provided is a means for improving cycle characteristics by suppressing electrode deterioration resulting from non-uniformity of voltage across an electrode plane in a high-capacity and large-area non-aqueous electrolyte secondary battery that includes lithium nickel-based composite oxide as a positive electrode active substance. 
     [Solving Means] Disclosed is a positive electrode for a non-aqueous electrolyte secondary battery used in a non-aqueous electrolyte secondary battery in which the ratio value of battery area (projected area of the battery including the battery outer casing body) to rated capacity is 5 cm 2 /Ah or more and the rated capacity is 3 Ah or more, the positive electrode comprising a positive electrode current collector and a positive electrode active substance layer that is formed on a surface of the positive electrode current collector and has a positive electrode active substance containing a lithium nickel-based composite oxide and a spinel type lithium manganese composite oxide, in which, when the average secondary particle diameter (D50) of the lithium nickel-based composite oxide is D50(A) [μm], the content ratio of the lithium nickel-based composite oxide in the positive electrode active substance layer is A [% by mass], the average secondary particle diameter (D50) of the spinel type lithium manganese composite oxide is D50(B) [μm], and the content ratio of the spinel type lithium manganese composite oxide in the positive electrode active substance layer is B [% by mass], the positive electrode satisfies the following Mathematical Formula 1 and Mathematical Formula 2:
 
[Math. 1]
 
0.5≦ D 50( A )/ D 50( B )≦2.0  MathematicalFormula1:
 
 B /( A+B )≧0.2  MathematicalFormula2:

TECHNICAL FIELD

The present invention relates to a positive electrode for a non-aqueouselectrolyte secondary battery and a non-aqueous electrolyte secondarybattery using the positive electrode.

BACKGROUND ART

Currently, a non-aqueous electrolyte secondary battery including alithium ion secondary battery, which is used for a mobile device such asa mobile phone, is available as a commercial product. The non-aqueouselectrolyte secondary battery generally has a constitution that apositive electrode having a positive electrode active substance or thelike coated on a current collector and a negative electrode having anegative electrode active substance or the like coated on a currentcollector are connected to each other via an electrolyte layer in whicha non-aqueous electrolyte solution or a non-aqueous electrolyte gel ismaintained within a separator. According to absorption and desorption ofions such as lithium ions on an electrode active substance, charging anddischarging reactions of a battery occur.

In recent years, it is desired to reduce the amount of carbon dioxide inorder to cope with the global warming. As such, a non-aqueouselectrolyte secondary battery having small environmental burden has beenused not only for a mobile device or the like but also for a powersource device of an electric vehicle such as a hybrid vehicle (HEV), anelectric vehicle (EV), and a fuel cell vehicle.

As the non-aqueous electrolyte secondary battery for application to anelectric vehicle, it is required to have high output and high capacity.As a positive electrode active substance used for the positive electrodeof a non-aqueous electrolyte secondary battery for an electric vehicle,a lithium cobalt-based composite oxide, which is a layered compositeoxide, has been already widely used since it can provide high voltage atthe level of 4 V and has high energy density. However, due to resourcescarcity, cobalt as a raw material is expensive, and considering thepossibility of having dramatic demand in future, it is not stable interms of supply of a raw material. There is also a possibility of havingan increase in the raw material cost of cobalt. Accordingly, a compositeoxide having less cobalt content ratio is desired.

A spinel type lithium manganese composite oxide (LiMn₂O₄) has a spinelstructure and it functions as a positive electrode material of 4 V gradeaccording to the composition with λ-MnO₂. By having a three dimensionalhost structure which is different from a layered structure of LiCoO₂ orthe like, most of the theoretical capacity of the spinel type lithiummanganese composite oxide is usable and it is expected to have excellentcycle characteristics.

However, with a lithium ion secondary battery in which the spinel typelithium manganese composite oxide is used as a positive electrodematerial, it is actually impossible to avoid capacity deteriorationwhich exhibits a gradual decrease in capacity according to repeatedcharge and discharge. As such, there has been a big problem for puttingit to practical use.

As a technique for solving the problem of capacity deterioration of aspinel type lithium manganese composite oxide, in JP 2000-77071 A, forexample, a technique of further using, as a positive electrode material,a lithium nickel-based composite oxide (LiNiO₂, Li₂NiO₂, LiNi₂O₄,Li₂Ni₂O₄, LiNi_(1-x)M_(x)O₂, or the like) with a predetermined specificsurface area in addition to a spinel type lithium manganese compositeoxide is disclosed. According to JP 2000-77071 A, it is described that,by having such constitution, dissolution of Mn from the spinel typelithium manganese composite oxide or a change in Li concentration in anelectrolyte solution is suppressed, and as a result, a non-aqueouselectrolyte secondary battery with highly improved charge and dischargecycle characteristics (in particular, charge and discharge service lifeat high temperature) can be provided.

SUMMARY OF INVENTION

According to the studies by the inventors of the present invention, itwas found that, even with the technique described in JP 2000-77071 A, ifa battery is produced to have high capacity and large area, sufficientcharge and discharge cycle characteristics are not achieved. It was alsofound that such a decrease in charge and discharge cycle characteristicsis caused by deterioration of an electrode in local over-charge mode,resulting from easy occurrence of non-uniformity of voltage across anelectrode plane by having a battery with high capacity and large area,which is caused by inclusion of a lithium nickel-based composite oxideas a positive electrode active substance.

Accordingly, the present invention is intended to provide a means forrealizing improvements in cycle characteristics by suppressing electrodedeterioration resulting from non-uniformity of voltage across anelectrode plane in a high-capacity and large-area non-aqueouselectrolyte secondary battery that includes a lithium nickel-basedcomposite oxide as a positive electrode active substance.

The inventors of the present invention conducted intensive studies. As aresult, it was found that the above problems can be solved when thespinel type lithium manganese composite oxide is used in combinationwith the lithium nickel-based composite oxide as a positive electrodeactive substance and an average secondary particle diameter and thecontent ratio thereof are controlled to a value within a predeterminedrange. The present invention is completed accordingly.

According to one embodiment of the present invention, a positiveelectrode for a non-aqueous electrolyte secondary battery used in anon-aqueous electrolyte secondary battery in which the ratio value ofbattery area (projected area of the battery including the battery outercasing body) to rated capacity is 5 cm²/Ah or more and the ratedcapacity is 3 Ah or more is provided. The positive electrode has apositive electrode current collector and a positive electrode activesubstance layer that is formed on a surface of the positive electrodecurrent collector and has a positive electrode active substancecontaining the lithium nickel-based composite oxide and the spinel typelithium manganese composite oxide. Furthermore, it is characterized inthat the positive electrode satisfies Mathematical Formula 1 andMathematical Formula 2 that are given below:[Math. 1]0.5≦D50(A)/D50(B)≦2.0  MathematicalFormula1:B/(A+B)≧0.2  MathematicalFormula2:

when the average secondary particle diameter (D50) of the lithiumnickel-based composite oxide is D50(A) [μm], the content ratio of thelithium nickel-based composite oxide in the positive electrode activesubstance layer is A [% by mass], the average secondary particlediameter (D50) of the spinel type lithium manganese composite oxide isD50(B) [μm], and the content ratio of the spinel type lithium manganesecomposite oxide in the positive electrode active substance layer is B [%by mass].

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a cross-sectional view schematically illustrating a basicconstitution of a non-aqueous electrolyte lithium ion secondary batterywhich is not a bipolar type of flat type (stack type) as one embodimentof the non-aqueous electrolyte lithium ion secondary battery.

FIG. 2 is a graph illustrating a charge curve of a lithium nickel-basedcomposite oxide such as an NMC composite oxide and a spinel type lithiummanganese composite oxide.

FIG. 3 is a graph illustrating the enlarged view of a region in terminalcharge state as shown in the charge curve of FIG. 2 (region X in FIG.2).

FIG. 4 is a perspective view illustrating outer appearance of a flatlithium ion secondary battery as a representative embodiment of asecondary battery.

FIG. 5 is a drawing to describe potential measurement points when a testcell produced in Examples is charged and disintegrated, the potential(relative to metal lithium) is measured at 5 points on a positiveelectrode active substance layer, and a difference between the maximumpotential and minimum potential is calculated as ΔV.

DESCRIPTION OF EMBODIMENT

According to one embodiment of the present invention, provided is apositive electrode for a non-aqueous electrolyte secondary battery foruse in a non-aqueous electrolyte secondary battery in which the ratio ofbattery area (projected area of the battery including the battery outercasing body) to rated capacity is 5 cm²/Ah or more and the ratedcapacity is 3 Ah or more, which has a positive electrode currentcollector and a positive electrode active substance layer that is formedon a surface of the positive electrode current collector and has apositive electrode active substance containing a lithium nickel-basedcomposite oxide and a spinel type lithium manganese composite oxide, andthe positive electrode for a non-aqueous electrolyte secondary batterysatisfies Mathematical Formula 1 and Mathematical Formula 2 that aregiven below when the average secondary particle diameter (D50) of thelithium nickel-based composite oxide is D50(A) [μm], the content ratioof the lithium nickel-based composite oxide in the positive electrodeactive substance layer is A [% by mass], the average secondary particlediameter (D50) of the spinel type lithium manganese composite oxide isD50(B) [μm], and the content ratio of the spinel type lithium manganesecomposite oxide in the positive electrode active substance layer is B [%by mass]:[Math. 2]0.5≦D50(A)/D50(B)≦2.0  MathematicalFormula1:B/(A+B)≧0.2  MathematicalFormula2:

According to the positive electrode for a non-aqueous electrolytesecondary battery of the present invention, the spinel type lithiummanganese composite oxide acts as an over-voltage promoter so that itcan increase the resistance around the spinel type lithium manganesecomposite oxide at a voltage near the upper voltage use limit of abattery, and thus an occurrence of local over-charge mode in anelectrode is suppressed. As a result, electrode deterioration resultingfrom non-uniformity of voltage across an electrode plane is preventedand it becomes possible to improve the cycle characteristics of anon-aqueous electrolyte secondary battery.

Next, descriptions are given for a non-aqueous electrolyte lithium ionsecondary battery as a preferred embodiment of the non-aqueouselectrolyte secondary battery to which the positive electrode of thepresent invention is applied, but it is not limited to the embodimentsdescribed below. Meanwhile, the same elements are given with the samesymbols for the descriptions of the drawings, and overlappeddescriptions are omitted. Further, note that dimensional ratios in thedrawings are exaggerated for the sake of explanation, and are differentfrom actual ratios in some cases.

FIG. 1 is a cross-sectional view schematically illustrating the basicconstitution of a non-aqueous electrolyte lithium ion secondary batterywhich is not a bipolar type of flat type (stack type) (hereinbelow, itis also simply referred to as a “stack type battery”). As illustrated inFIG. 1, a stack type battery 10 according to this embodiment has astructure in which the power generating element 21 with a substantiallyrectangular shape, in which a charge and discharge reaction actuallyoccurs, is sealed inside of a battery outer casing material 29 as anouter casing body. Herein, the power generating element 21 has aconstitution in which a positive electrode, a separator 17, and anegative electrode are stacked. Meanwhile, the separator 17 has anon-aqueous electrolyte (for example, liquid electrolyte) therein. Thepositive electrode has a structure in which the positive electrodeactive substance layer 15 is disposed on both surfaces of the positiveelectrode current collector 12. The negative electrode has a structurein which the negative electrode active substance layer 13 is disposed onboth surfaces of the negative electrode current collector 11.Specifically, one positive electrode active substance layer 15 and theneighboring negative electrode active substance layer 13 are disposed toface each other via the separator 17, and a negative electrode, anelectrolyte layer and a positive electrode are stacked in this order.Accordingly, the neighboring positive electrode, electrolyte layer andnegative electrode form one single battery layer 19. As such, it canalso be said that, as plural single barrier layers 19 are stacked, thestack type battery 10 illustrated in FIG. 1 has a constitution in whichelectrically parallel connection is made among them.

Meanwhile, on the outermost layer positive electrode current collectorwhich is present on both outermost layers of the power generatingelement 21, the negative electrode active substance layer 13 is disposedonly on a single surface. However, an active substance layer may beformed on both surfaces. Namely, not only a current collector exclusivefor an outermost layer in which an active substance layer is formed onlyon a single surface can be prepared but also a current collector havingan active substance layer on both surfaces can be directly used as acurrent collector of an outermost layer. Furthermore, by reversing thearrangement of the positive electrode and negative electrode of FIG. 1,it is also possible that the outermost layer positive electrode currentcollector is disposed on both outermost layers of the power generatingelement 21 and a positive electrode active substance layer is disposedon a single surface or both surfaces of the outermost layer positiveelectrode current collector.

The positive electrode current collector 12 and negative electrodecurrent collector 11 have a structure in which each of the positiveelectrode current collecting plate (tab) 27 and negative electrodecurrent collecting plate (tab) 25, which conductively communicate witheach electrode (positive electrode and negative electrode), is attachedand inserted to a terminal of the battery outer casing material 29 so asto be led to the outside of the battery outer casing material 29. Ifnecessary, each of the positive electrode current collecting plate 27and negative electrode current collecting plate 25 can be attached, viaa positive electrode lead and negative electrode lead (not illustrated),to the positive electrode current collector 11 and negative electrodecurrent collector 12 of each electrode by ultrasonic welding orresistance welding.

Meanwhile, although a stack type battery is illustrated in FIG. 1instead of a bipolar type of flat type (stack type), it can also be abipolar type battery containing a bipolar type electrode which has apositive electrode active substance layer electrically bound to onesurface of a current collector and a negative electrode active substancelayer electrically bound to the opposite surface of a current collector.In that case, one current collector plays both roles of a positiveelectrode current collector and a negative electrode current collector.

Hereinbelow, each member is described in more detail.

[Positive Electrode]

The positive electrode has a positive electrode current collector and apositive electrode active substance layer that is formed on a surface ofthe positive electrode current collector.

(Positive Electrode Current Collector)

The material for constituting a positive electrode current collector isnot particularly limited, but a metal is preferably used. Specificexamples of the metal include aluminum, nickel, iron, stainless, titan,copper, and other alloys. In addition to them, a clad material of anickel and aluminum, a clad material of copper and aluminum, or aplating material of a combination of those metals can be preferablyused. It can also be a foil obtained by coating aluminum on a metalsurface. Among them, from the viewpoint of electron conductivity orpotential for operating a battery, aluminum, stainless, and copper arepreferable.

The size of the current collector is determined based on use of abattery. When it is used for a large-size battery which requires highenergy density, for example, a current collector with large area isused. Thickness of the current collector is not particularly limited,either. Thickness of the current collector is generally 1 to 100 μm orso.

(Positive Electrode Active Substance Layer)

The positive electrode active substance layer contains a positiveelectrode active substance. According to this embodiment, the positiveelectrode active substance essentially contains lithium nickel-basedcomposite oxide and spinel type lithium manganese composite oxide.Meanwhile, the ratio of the total amount of lithium nickel-basedcomposite oxide and spinel type lithium manganese composite oxiderelative to the whole amount of 100% by weight of the positive electrodeactive substance contained in the positive electrode active substancelayer is preferably 50% by weight or more, more preferably 70% by weightor more, even more preferably 85% by weight or more, still even morepreferably 90% by weight or more, particularly preferably 95% by weightor more, and most preferably 100% by weight.

Lithium Nickel-Based Composite Oxide

The lithium nickel-based composite oxide is not specifically limited interms of the composition as long as it is a composite oxide containinglithium and nickel. Representative examples of the composite oxidecontaining lithium and nickel include a lithium nickel composite oxide(LiNiO₂). However, a composite oxide in which part of the nickel atomsof the lithium nickel composite oxide is replaced with another metalatom is more preferable. As a preferable example, alithium-nickel-manganese-cobalt composite oxide (hereinbelow, alsosimply referred to as “NMC composite oxide”) has a layered crystalstructure in which a lithium atom layer and a transition metal (Mn, Ni,and Co are arranged with regularity) atom layer are alternately stackedvia an oxygen atom layer, one Li atom is included per atom of transitionmetal M and extractable Li amount is twice the amount of spinel typelithium manganese oxide, that is, as the supply power is two timeshigher, it can have high capacity. In addition, as having higher heatstability compared to LiNiO₂, it is particularly advantageous among thenickel-based composite oxides that are used as a positive electrodeactive substance.

As described herein, the NMC composite oxide includes a composite oxidein which part of transition metal elements are replaced with anothermetal element. In that case, examples of another element include Ti, Zr,Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu,Ag, and Zn. Preferably, it is Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, orCr. More preferably, it is Ti, Zr, P, Al, Mg, or Cr. From the viewpointof improving the cycle characteristics, it is even more preferably Ti,Zr, Al, Mg, or Cr.

By having high theoretical discharge capacity, the NMC composite oxidepreferably has a composition represented by General Formula (1):Li_(a)Ni_(b)Mn_(c)Co_(d)M_(x)O₂ (with the proviso that, in the formula,a, b, c, d, and x satisfy 0.9≦a≦1.2, 0<b<1, 0<c≦0.5, 0<d≦0.5, 0≦x≦0.3,and b+c+d=1. M represents at least one element selected from Ti, Zr, Nb,W, P, Al, Mg, V, Ca, Sr, and Cr). Herein, a represents the atomic ratioof Li, b represents the atomic ratio of Ni, c represents the atomicratio of Mn, d represents the atomic ratio of Co, and x represents theatomic ratio of M. From the viewpoint of the cycle characteristics, itis preferable that 0.4≦b≦0.6 in the General Formula (1). Meanwhile,composition of each element can be measured, for example, by inductioncoupled plasma (ICP) spectroscopy.

In general, from the viewpoint of improving purity and improvingelectron conductivity of a material, nickel (Ni), cobalt (Co) andmanganese (Mn) are known to contribute to capacity and outputcharacteristics. Ti or the like replaces part of transition metal in acrystal lattice. From the viewpoint of the cycle characteristics, it ispreferable that part of transition element are replaced by another metalelement, and it is preferable that 0<x≦0.3 is satisfied in the GeneralFormula (1), in particular. It is believed that the crystal structure isstabilized by dissolving at least one selected from the group consistingof Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr so that decrease incapacity of a battery can be prevented even after repeated charge anddischarge, and thus, excellent cycle characteristics can be achieved.

With regard to the NMC composite oxide, the inventors of the presentinvention found that the influence of deformation and cracking of acomposite oxide during charge and discharge described above becomeshigher if the metal composition of nickel, manganese and cobalt isheterogeneous like LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂. This is believedbecause, as the metal composition is heterogeneous, deformation iscaused in stress applied to the inside of a particle during expansionand shrinkage so that cracks are more easily generated in the compositeoxide. Thus, when comparison is made with, for example, a compositeoxide having a rich Ni abundance ratio (for example,LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂) or a composite oxide with a homogenousabundance ratio of Ni, Mn and Co (for example,LiNi_(0.3)Mn_(0.3)Co_(0.3)O₂), more significant decrease in long-termcycle characteristics is yielded. By having the structure according tothis embodiment, it was found that the cycle characteristics aresurprisingly improved even for a composite oxide having a heterogeneousmetal composition like LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂.

Thus, the positive electrode active substance with a composite oxide inwhich b, c, and d in the General Formula (1) satisfy 0.44≦b≦0.51,0.27≦c≦0.31, and 0.19≦d≦0.26 is preferable in that the effect of thepresent invention is obtained at significant level.

The lithium nickel-based composite oxide has a structure of secondaryparticles formed by aggregation of primary particles. In addition, theaverage particle diameter of the primary particles (average primaryparticle diameter) is preferably 0.9 μm or less, more preferably 0.20 to0.6 μm and even more preferably 0.25 to 0.5 μm. In addition, the averageparticle diameter of the secondary particles (average secondary particlediameter, also referred to as “D50(A)” as described herein) ispreferably 5 to 20 μm, and more preferably 5 to 15 μm. In addition, itis sufficient that the ratio value thereof (the average secondaryparticle diameter/the average primary particle diameter) is higher than11. Preferably, it is 15 to 50, and more preferably 25 to 40. Meanwhile,the primary particles forming the lithium nickel-based composite oxidegenerally have a crystal structure of hexagonal crystal package withlayered structure. The largeness of the diameter of crystallite isrelated to the largeness of the average primary particle diameter. Asdescribed herein “crystallite” indicates the largest group which can bedetermined as a monocrystal, and it can be measured by the method ofrefining structure parameters of a crystal from diffraction intensitythat is obtained by powder X ray diffraction measurement or the like.The specific value of the crystallite diameter is, although notparticularly limited, preferably 1 μm or less, more preferably 0.55 μmor less, and even more preferably 0.4 μm or less. By having such astructure, the displacement amount involved with shrinkage and expansionof an active substance can be further reduced and an occurrence ofmicronization (cracking) of the secondary particles accompanyingrepetition of charge and discharge is inhibited, which can furthercontribute to improvement of the cycle characteristics. Meanwhile, thelower limit of the crystallite diameter is, although not particularlylimited, generally 0.02 μm or more. In the present specification, thevalues of the average primary particle diameter, the average secondaryparticle diameter (D50(A)) and the crystallite diameter of the lithiumnickel-based composite oxide can be measured by known methods, and inparticular, regarding the average secondary particle diameter and thecrystallite diameter, the value measured by the method described beloware used.

Namely, as for the measurement of the average secondary particlediameter (D50(A)), the value measured by laser diffraction method isused. Furthermore, the crystallite diameter was measured by Rietveldmethod by which crystallite diameter is calculated from diffraction peakintensity obtained by powder X ray diffraction measurement.

The tap density of the lithium nickel-based composite oxide ispreferably 2.3 g/cm³ or more, and more preferably 2.4 to 2.9 g/cm³. Byhaving such a structure, high density of the primary particles formingthe secondary particles of the positive electrode active substance issufficiently ensured, and thus the effect of improving the cyclecharacteristics can be maintained.

In addition, the BET specific surface area of the lithium nickel-basedcomposite oxide is preferably 0.1 to 1.0 m²/g, more preferably 0.3 to1.0 m²/g, and particularly preferably 0.3 to 0.7 m²/g. As the specificsurface area of the active substance is within this range, the reactionarea of the active substance is ensured so that the internal resistanceof a battery is lowered. As a result, an occurrence of polarization canbe suppressed at minimum level at the time of an electrode reaction.

Furthermore, regarding the lithium nickel-based composite oxide, thediffraction peak of a (104) surface and the diffraction peak of a (003)surface which are obtained by powder X ray diffraction measurement, havea diffraction peak intensity ratio ((003)/(104)) of preferably 1.28 ormore and more preferably 1.35 to 2.1. Furthermore, the diffraction peakintegrated intensity ratio ((003)/(104)) is preferably 1.08 or more andmore preferably 1.10 to 1.45. Those requirements are preferred due tothe following reasons. Specifically, the lithium nickel-based compositeoxide has a layered rock salt structure in which Li⁺ layer and Ni³⁺layer are present between oxygen layers. However, as Ni³⁺ is easilyreduced to Ni²⁺ and the ionic radius of Ni²⁺ (0.83 A) is substantiallyequal to the ionic radius of Li⁺ (0.90 A), it is easy for Ni²⁺ to beincorporated into a Li⁺ defect site which is generated during synthesisof the active substance. Once Ni²⁺ is incorporated into the Li⁺ site, anelectrochemically unstable structure is formed locally, and alsodiffusion of Li⁺ is inhibited. For such reasons, when an activesubstance with low crystallinity is used, there is a possibility thatthe battery charge and discharge capacity is lowered or durability isimpaired. Thus, as an indicator of this crystallinity, theaforementioned requirements are employed. Herein, as a method forquantifying the crystallinity, the diffraction peak intensity ratio of a(003) surface to a (104) surface and the integrated intensity ratio ofdiffraction peak, based on crystal structure analysis using X raydiffraction as described above, were used. When these parameters satisfythe above requirements, there are fewer defects within a crystal so thata decrease in battery charge and discharge capacity or impairment ofdurability can be suppressed. Meanwhile, the parameters of crystallinitycan be controlled based on a raw material, a composition, conditions forcalcination or the like.

The lithium nickel-based composite oxide such as the NMC composite oxidecan be produced by selecting various known methods such as aco-precipitation method and a spray drying method. From the viewpoint ofhaving easy production of the composite oxide according to thisembodiment, a co-precipitation method is preferably used. Specifically,with regard to a method for synthesizing the NMC composite oxide,production can be made by, for example, a method described in JP2011-105588 A in which a nickel-cobalt-manganese composite oxide isproduced by the co-precipitation method and the nickel-cobalt-manganesecomposite oxide is admixed with a lithium compound followed bycalcination. Specific descriptions are given hereinbelow.

Raw material compounds of a composite oxide, for example, a Ni compound,a Mn compound, or a Co compound, are dissolved in a suitable solventsuch as water so as to have a desired composition of an active substancematerial. Examples of the Ni compound, the Mn compound and the Cocompound include sulfate, nitrate, carbonate, acetate, oxalate, oxide,hydroxide, and halide of the metal element. Specific examples of the Nicompound, the Mn compound and the Co compound include nickel sulfate,cobalt sulfate, manganese sulfate, nickel acetate, cobalt acetate, andmanganese acetate, but not limited thereto. During the process, ifnecessary, in order to have a further desired composition of an activesubstance, a compound containing at least one metal element such as Ti,Zr, Nb, W, P, Al, Mg, V, Ca, Sr or Cr as a metal element for replacingpart of the layered lithium metal composite oxide which forms the activesubstance may be further incorporated.

A co-precipitation reaction can be performed by neutralization andprecipitation reactions using the above raw material compounds and analkali solution. Accordingly, metal composite hydroxide or metalcomposite carbonate containing the metal included in the above rawmaterial compounds can be obtained. Examples of the alkali solutionwhich can be used include an aqueous solution of sodium hydroxide,potassium hydroxide, sodium carbonate, or ammonia. For theneutralization reaction, it is preferable to use sodium hydroxide,sodium carbonate, or a mixture solution thereof. In addition, it ispreferable to use an aqueous ammonia solution or ammonia salt for acomplex reaction.

The addition amount of the alkali solution used for neutralizationreaction is sufficient to have the equivalent ratio of 1.0 to componentsto be neutralized which are contained in the whole metal salts. However,for having pH control, it is preferably added together with an excessalkali amount.

The aqueous ammonia solution or ammonia salt used for a complex reactionis preferably added such that the ammonia concentration in the reactionsolution is in a range of 0.01 to 2.00 mol/l. The pH of the reactionsolution is preferably controlled in a range of 10.0 to 13.0. Thereaction temperature is preferably 30° C. or higher, and more preferably30 to 60° C.

The composite hydroxide obtained by co-precipitation reaction is thenpreferably filtered by suction, washed with water, and dried. Meanwhile,by controlling the conditions for performing the co-precipitationreaction (for example, stirring time and alkali concentration), particlediameter of the composite hydroxide can be controlled, and it has aninfluence on the average particle diameter of the secondary particles(D50(A)) of a positive electrode active substance which is finallyobtained.

Subsequently, by mixing and calcining nickel-cobalt-manganese compositehydroxide with a lithium compound, the lithium-nickel-manganese-cobaltcomposite oxide can be obtained. Examples of the Li compound includelithium hydroxide or a hydrate thereof, lithium peroxide, lithiumnitrate and lithium carbonate.

The calcination treatment can be performed by one step, but it ispreferably performed by two steps (temporary calcination and maincalcination). According to two-step calcination, a composite oxide canbe obtained efficiently. The conditions for temporary calcination arenot particularly limited, and they may vary depending on the lithium rawmaterial, and thus cannot be unambiguously defined. Here, as the factorsfor controlling D1 (and also D2/D1) and crystallite diameter inparticular, calcination temperature and calcination time for calcination(temporary calcination and main calcination in the case of a two-stepcalcination) are particularly important. By making a control of thembased on the tendency described below, D1 (and also D2/D1) and thecrystallite diameter can be controlled. Namely, D1 and crystalliteparticle diameter are increased by having longer calcination time. D1and crystallite particle diameter are also increased by increasing thecalcination temperature. Meanwhile, the temperature increase rate ispreferably 1 to 20° C./minute from room temperature. Furthermore, theatmosphere is preferably either air or oxygen atmosphere. Here, when theNMC composite oxide is synthesized by using lithium carbonate as the Liraw material, temperature for temporary calcination is preferably 500 to900° C., more preferably 600 to 800° C., and even more preferably 650 to750° C. Furthermore, time for temporary calcination is preferably 0.5 to10 hours and more preferably 4 to 6 hours. Meanwhile, as for theconditions for main calcination, the temperature increase rate ispreferably 1 to 20° C./minute from room temperature, although it is notparticularly limited thereto. Furthermore, the atmosphere is preferablyeither air or oxygen atmosphere. Here, when the NMC composite oxide issynthesized by using lithium carbonate as the Li raw material,temperature for calcination is preferably 800 to 1200° C., morepreferably 850 to 1100° C., and even more preferably 900 to 1050° C.Furthermore, time for calcination is preferably 1 to 20 hours and morepreferably 8 to 12 hours.

When a tiny amount of a metal element for replacing part of the layeredlithium metal composite oxide forming an active substance material isadded as needed, any means such as mixing it in advance with nickel,cobalt, manganate salt, adding it simultaneously with nickel, cobalt,manganate salt, adding it to a reaction solution during the reaction, oradding it to the nickel-cobalt-manganese composite oxide with a Licompound can be employed.

The lithium nickel-based composite oxide can be produced by suitablycontrolling the reaction conditions such as pH of a reaction solution,reaction temperature, reaction concentration, addition rate, and timefor stirring.

Spinel Type Lithium Manganese Composite Oxide

The spinel type lithium manganese composite oxide typically hascomposition of LiMn₂O₄, and it is the composite oxide with spinelstructure which essentially contains lithium and manganese. As for thespecific constitution or production method, reference can be suitablymade to disclosure of a related art such as JP 2000-77071 A.

The spinel type lithium manganese composite oxide also has aconstitution that the secondary particles are formed by aggregation ofprimary particles. Furthermore, the average particle diameter ofsecondary particles (average secondary particle diameter) is preferably5 to 50 μm, and more preferably 7 to 20 μm.

One characteristic of the positive electrode for a non-aqueouselectrolyte secondary battery according to this embodiment is that theaverage secondary particle diameter of lithium nickel-based compositeoxide (D50(A)) and the average secondary particle diameter of spineltype lithium manganese composite oxide (D50(B)), both being constituentsof a positive electrode active substance contained in a positiveelectrode active substance layer, satisfy the following MathematicalFormula 1.[Math. 3]0.5≦D50(A)/D50(B)≦2.0  MathematicalFormula1:

Meanwhile, the ratio value of D50(A)/D50(B) preferably satisfies therelationship of 0.67≦D50(A)/D50(B)≦1.5.

Furthermore, other characteristic of the positive electrode for anon-aqueous electrolyte secondary battery according to this embodimentis that the content ratio of the lithium nickel-based composite oxide inthe positive electrode active substance layer (A [% by weight]) and thecontent ratio of the spinel type lithium manganese composite oxide inthe positive electrode active substance layer (B [% by weight]) satisfyfollowing Mathematical Formula 2:[Math. 4]B/(A+B)≧0.2  MathematicalFormula2:

Namely, the characteristic is that the ratio of spinel type lithiummanganese composite oxide in the total amount of above two types is 20%by weight or more. Meanwhile, A and B preferably satisfy therelationship of 0.2≦B/(A+B)≦0.8, and more preferably the relationship of0.3≦B/(A+B)≦0.5.

Since the positive electrode for a non-aqueous electrolyte secondarybattery of this embodiment has the constitution described above, cyclecharacteristics can be improved as the electrode deterioration caused bynon-uniformity of voltage across an electrode plane is suppressed whenit is applied to a non-aqueous electrolyte secondary battery with highcapacity and large area. The mechanism believed to be involved withexhibition of such excellent effects is described below in view of FIG.2 and FIG. 3. FIG. 2 is a graph illustrating a charge curve of lithiumnickel-based composite oxide such as an NMC composite oxide and a spineltype lithium manganese composite oxide. Furthermore, FIG. 3 is a graphillustrating the enlarged view of a region in terminal charge state asshown in the charge curve of FIG. 2 (region X in FIG. 2). Herein, thecharge curve illustrated in FIG. 2 and FIG. 3 is expressed as a graph inwhich active substance capacity (SOC(State of Charge); charge state [%])is described on the horizontal axis and cell voltage [V] is described onthe vertical axis. Meanwhile, the charge curve illustrated in FIG. 2 andFIG. 3 is plotted by performing charge of a battery in constant-currentmode up to predetermined cut off voltage (for example, 4.25 V in termsof cell voltage).

As illustrated in FIG. 2 and FIG. 3, the lithium nickel-based compositeoxide and spinel type lithium manganese composite oxide generallyexhibit a different behavior in a terminal charge state in charge curve.Specifically, a lithium nickel-based composite oxide exhibits a chargecurve in which the active substance capacity increases and SOC appearsto continuously increase (almost linearly) according to progress ofcharge (increased cell voltage) even in a terminal charge state. On theother hand, a spinel type lithium manganese composite oxide exhibits,starting from some point in the terminal charge state, a charge curve inwhich the increase rate of the active substance capacity appears todiminish compared to the progress of charge (increased cell voltage).Since such behavior exhibited by the spinel type lithium manganesecomposite oxide is referred to as “over-voltage”, the spinel typelithium manganese composite oxide is designated as an “over-voltagepromoter” in the present specification.

As described above, according to the studies by the inventors of thepresent invention, it was found that, even with the technique describedin JP 2000-77071 A, if a battery is produced to have high capacity andlarge area, sufficient charge and discharge cycle characteristics arenot achieved. As a result of investigation of the reasons for that, itwas also found by the inventors of the present invention thatnon-uniformity of voltage occurs across an electrode plane as thebattery is prepared to have high capacity and large area, although ithas not occurred in a battery such as an everyday household batterywhich has low capacity and small area. Accordingly, it was speculatedthat, if a lithium nickel-based composite oxide, which causes an activesubstance capacity increase according to progress of charge (increasedcell voltage) even in a terminal charge state, is contained in apositive electrode active substance, due to the non-uniformity ofvoltage across an electrode plane (voltage width across plane), adeviation in charge state occurs among the lithium nickel-basedcomposite oxides of the same type as illustrated in FIG. 3. It was thenhypothesized that local over-charge mode is established in the lithiumnickel-based composite oxide with more progressed charge state, and as aresult of deterioration of that composite oxide first, a decrease incharge and discharge cycle characteristics is caused. It was alsohypothesized that, as Joule heat generated according to charge is noteasily dissipated to an outside for a battery with high capacity andlarge area, inside of an electrode is full of heat, causing morenon-uniformity of voltage across an electrode plane.

It was also speculated the occurrence of an over-charge mode of lithiumnickel-based composite oxide described above could be suppressed if aspinel type lithium manganese composite oxide capable of functioning asan over-voltage promoter is used, as a positive electrode activesubstance, in combination with a lithium nickel-based composite oxide.Thus, further investigations were carried out. As a result, it was foundthat, when a spinel type lithium manganese composite oxide as anover-voltage promoter is contained at the content ratio of theaforementioned predetermined amount or higher in a positive electrodeactive substance after adjusting the ratio of the average secondaryparticle diameter of each composite oxide to a value within apredetermined range, a decrease in charge and discharge cyclecharacteristics is suppressed. Furthermore, with the battery of thisembodiment, alleviation of the non-uniformity of voltage across anelectrode plane is confirmed, and thus the legitimacy of theaforementioned hypothesis was shown with evidence and the presentinvention was completed accordingly.

Other Components

If necessary, the positive electrode active substance layer furthercontains, in addition to the aforementioned positive electrode activesubstance, other additives such as a conductive aid, a binder, anelectrolyte (for example, polymer matrix, ion conductive polymer, andelectrolyte solution), and lithium salt for enhancing ion conductivity.However, the content of a material capable of functioning as an activesubstance in the positive electrode active substance layer and thenegative electrode active substance layer described below is preferably85 to 99.5% by weight.

(Binder)

A binder used for the positive electrode active substance layer is notparticularly limited and the following materials can be mentioned;thermoplastic polymers such as polyethylene, polypropylene, polyethyleneterephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide,polyamide, cellulose, carboxymethyl cellulose (CMC) and a salt thereof,an ethylene-vinyl acetate copolymer, polyvinylidene chloride,styrene-butadiene rubber (SBR), isoprene rubber, butadiene rubber,ethylene-propylene rubber, an ethylene-propylene-diene copolymer, astyrene-butadiene-styrene block copolymer and a hydrogen-added productthereof, and a styrene-isoprene-styrene block copolymer and ahydrogen-added product thereof, fluorine resins such as polyvinylidenefluoride (PVdF), polytetrafluoroethylene (PTFE), atetrafluoroethylene-hexafluoropropylene copolymer (FEP), atetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), anethylene-tetrafluoroethylene copolymer (ETFE),polychlorotrifluoroethylene (PCTFE), an ethylene-chlorotrifluoroethylenecopolymer (ECTFE), and polyvinyl fluoride (PVF), vinylidenefluoride-based fluorine rubber such as vinylidenefluoride-hexafluoropropylene-based fluorine rubber (VDF-HFP-basedfluorine rubber), vinylidenefluoride-hexafluoropropylene-tetrafluoroethylene-based fluorine rubber(VDF-HFP-TFE-based fluorine rubber), vinylidenefluoride-pentafluoropropylene-based fluorine rubber (VDF-PFP-basedfluorine rubber), vinylidenefluoride-pentafluoropropylene-tetrafluoroethylene-based fluorine rubber(VDF-PFP-TFE-based fluorine rubber), vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylene-based rubber (VDF-PFMVE-TFE-basedfluorine rubber), and vinylidene fluoride-chlorotrifluoroethylenefluorine-based rubber (VDF-CTFE-based fluorine rubber), an epoxy resin,and the like. These binders may be each used singly, or two or morethereof may be used in combination.

The amount of the binder contained in the positive electrode activesubstance layer is not particularly limited as long as the binder canbind the active substance. The amount of binder is preferably 0.5 to 15%by weight, more preferably 1 to 10% by weight with respect to the activesubstance layer.

If necessary, the positive electrode active substance layer furthercontains other additives such as a conductive aid, an electrolyte (forexample, polymer matrix, ion conductive polymer, and electrolytesolution), and lithium salt for enhancing ion conductivity.

The conductive aid means an additive which is blended in order toenhance the conductivity of the positive electrode active substancelayer or negative electrode active substance layer. Examples of theconductive aid include carbon materials such as carbon black includingketjen black and acetylene black; graphite; and carbon fiber. When theactive substance layer contains a conductive aid, an electron network inthe inside of the active substance layer is formed effectively, and itcan contribute to improvement of the output characteristics of abattery.

Examples of the electrolyte salt (lithium salt) include Li(C₂F₅SO₂)₂N,LiPF₆, LiBF₄, LiClO₄, LiAsF₆, and LiCF₃SO₃.

Examples of the ion conductive polymer include polyethylene oxide(PEO)-based and polypropylene oxide (PPO)-based polymer.

A blending ratio of the components that are contained in the positiveelectrode active substance layer and negative electrode active substancelayer described below is not particularly limited. The blending ratiocan be adjusted by suitably referring to the already-known knowledgeabout a lithium ion secondary battery. The thickness of each activesubstance layer is not particularly limited either, and reference can bemade to the already-known knowledge about a battery. For example, thethickness of each active substance layer is about 2 to 100 μm.

[Negative Electrode Active Substance Layer]

The negative electrode active substance layer contains an activesubstance, and if necessary, further contains other additives such as aconductive aid, a binder, an electrolyte (for example, polymer matrix,ion conductive polymer, and electrolyte solution), and lithium salt forenhancing ion conductivity. The other additives such as a conductiveaid, a binder, an electrolyte (for example, polymer matrix, ionconductive polymer, and electrolyte solution), and lithium salt forenhancing ion conductivity are the same as those described above for thepositive electrode active substance layer.

Examples of the negative electrode active substance include a carbonmaterial such as graphite, soft carbon, and hard carbon, alithium-transition metal composite oxide (for example, Li₄Ti₅O₁₂), ametal material, and a lithium alloy-based negative electrode material.If necessary, two or more kinds of a negative electrode active substancemay be used in combination. Preferably, from the viewpoint of capacityand output characteristics, a carbon material or a lithium-transitionmetal composite oxide is used as a negative electrode active substance.Meanwhile, it is needless to say that a negative electrode activesubstance other than those described above can be also used.

The average particle diameter of a negative electrode active substanceis, although not particularly limited, preferably 1 to 100 μm, and morepreferably 1 to 20 μm from the viewpoint of having high output.

The negative electrode active substance layer preferably contains atleast an aqueous binder. The aqueous binder has a high binding property.Further, since water as a raw material is easily available and also onlywater vapor is generated during drying, there is an advantage that theinvestment on facilities of a production line can be greatly reduced andan environmental load can be reduced.

The aqueous binder indicates a binder which has water as a solvent or adispersion medium, and specific examples thereof include a thermoplasticresin, a polymer with rubber elasticity, a water soluble polymer, and amixture thereof. Herein, the binder which has water as a dispersionmedium includes all expressed as latex or an emulsion, and it indicatesa polymer emulsified in water or suspended in water. Examples thereofinclude a polymer latex obtained by emulsion polymerization in aself-emulsifying system.

Specific examples of the aqueous binder include a styrene polymer(styrene-butadiene rubber, styrene-vinyl acetic acid copolymer,styrene-acryl copolymer or the like), acrylonitrile-butadiene rubber,methacrylic acid methyl-butadiene rubber, (meth)acrylic polymer(polyethylacrylate, polyethylmethacrylate, polypropylacrylate,polymethylmethacrylate (methacrylic acid methyl rubber),polypropylmethacrylate, polyisopropylacrylate,polyisopropylmethacrylate, polybutylacrylate, polybutylmethacrylate,polyhexylacrylate, polyhexylmethacrylate, polyethylhexylacrylate,polyethylhexylmethacrylate, polylaurylacrylate, polylaurylmethacrylate,or the like), polytetrafluoroethylene, polyethylene, polypropylene, anethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber,polyethylene oxide, polyepichlorohydrin, polyphosphagen,polyacrylonitrile, polystyrene, an ethylene-propylene-diene copolymer,polyvinylpyridine, chlorosulfonated polyethylene, a polyester resin, aphenol resin, an epoxy resin; polyvinyl alcohol (average polymerizationdegree is preferably 200 to 4000, and more preferably 1000 to 3000, andsaponification degree is preferably 80% by mol or more, and morepreferably 90% by mol or more) and a modified product thereof (1 to 80%by mol saponified product in a vinyl acetate unit of a copolymer withethylene/vinyl acetate=2/98 to 30/70 (molar ratio), Ito 50% by molpartially acetalized product of polyvinyl alcohol, or the like), starchand a modified product (oxidized starch, phosphoric acid esterifiedstarch, cationized starch, or the like), cellulose derivatives(carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose,hydroxyethyl cellulose, and a salt thereof), polyvinylpyrrolidone,polyacrylic acid (salt), polyethylene gylcol, a copolymer of(meth)acrylamide and/or (meth)acrylic acid salt [(meth)acrylamidepolymer, (meth)acrylamide-(meth) acrylic acid salt copolymer, alkyl(meth) acrylic acid (carbon atom number of 1 to 4) ester-(meth) acrylicacid salt copolymer, or the like], a styrene-maleic acid salt copolymer,a mannich modified product of polyacrylamide, a formalin condensationtype resin (urea-formalin resin, melamin-formalin resin or the like), apolyamidepolyamine or dialkylamine-epichlorohydrin copolymer,polyethyleneimine, casein, soybean protein, synthetic protein, and awater soluble polymer such as galactomannan derivatives. The aqueousbinder can be used either singly or in combination of two or more types.

From the viewpoint of a binding property, the aqueous binder preferablycontains at least one rubber-based binder selected from a groupconsisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber,methacrylic acid methyl-butadiene rubber, and methacrylic acid methylrubber. Further, from the viewpoint of having a good binding property,the aqueous binder preferably contains styrene-butadiene rubber.

When styrene-butadiene rubber is used as an aqueous binder, theaforementioned water soluble polymer is preferably used in combinationfrom the viewpoint of improving the coating property. Examples of thewater soluble polymer which is preferably used in combination withstyrene-butadiene rubber include polyvinyl alcohol and a modifiedproduct thereof, starch and a modified product thereof, cellulosederivatives (carboxymethyl cellulose, methyl cellulose, hydroxyethylcellulose, and a salt thereof), polyvinylpyrrolidone, polyacrylic acid(salt), and polyethylene glycol. Among them, styrene-butadiene rubberand carboxymethyl cellulose (salt) are preferably combined as a binder.The weight content ratio between styrene-butadiene rubber and a watersoluble polymer is, although not particularly limited, preferably asfollows: styrene-butadiene rubber:water soluble polymer=1:0.1 to 10, andmore preferably 1:0.5 to 2.

In a binder used for the negative electrode active substance layer, thecontent of the aqueous binder is preferably 80 to 100% by weight,preferably 90 to 100% by weight, and preferably 100% by weight.

[Separator (Electrolyte Layer)]

A separator has a function of maintaining an electrolyte to ensurelithium ion conductivity between a positive electrode and a negativeelectrode and also a function of a partition wall between a positiveelectrode and a negative electrode.

Examples of a separator shape include a porous sheet separator or anon-woven separator composed of a polymer or a fiber which absorbs andmaintains the electrolyte.

As a porous sheet separator composed of a polymer or a fiber, amicroporous (microporous membrane) separator can be used, for example.Specific examples of the porous sheet composed of a polymer or a fiberinclude a microporous (microporous membrane) separator which is composedof polyolefin such as polyethylene (PE) and polypropylene (PP); alaminate in which plural of them are laminated (for example, a laminatewith three-layer structure of PP/PE/PP), and a hydrocarbon based resinsuch as polyimide, aramid, or polyfluorovinylydene-hexafluoropropylene(PVdF-HFP), or glass fiber.

The thickness of the microporous (microporous membrane) separator cannotbe uniformly defined as it varies depending on use of application. Forexample, for an application in a secondary battery for operating a motorof an electric vehicle (EV), a hybrid electric vehicle (HEV), a fuelcell vehicle (FCV) or the like, it is preferably 4 to 60 μm as amonolayer or a multilayer. Fine pore diameter of the microporous(microporous membrane) separator is preferably 1 μm or less at most (ingeneral, the pore diameter is about several tens of nanometers).

As a non-woven separator, conventionally known ones such as cotton,rayon, acetate, nylon, polyester; polyolefin such as PP and PE;polyimide and aramid are used either singly or as a mixture.Furthermore, the volume density of a non-woven fabric is notparticularly limited as long as sufficient battery characteristics areobtained with an impregnated polymer gel electrolyte. Furthermore, it issufficient that the thickness of the non-woven separator is the same asthat of an electrolyte layer. Preferably, it is 5 to 200 μm.Particularly preferably, it is 10 to 100 μm.

As described above, the separator also contains an electrolyte. Theelectrolyte is not particularly limited if it can exhibit thosefunctions, and a liquid electrolyte or a gel polymer electrolyte isused. By using a gel polymer electrolyte, a distance between electrodesis stabilized and an occurrence of polarization is suppressed so thatthe durability (cycle characteristics) is improved.

The liquid electrolyte has an activity of a lithium ion carrier. Theliquid electrolyte constituting an electrolyte solution layer has theform in which lithium salt as a supporting salt is dissolved in anorganic solvent as a plasticizer. Examples of the organic solvent whichcan be used include carbonates such as ethylene carbonate (EC),propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate(DEC), and ethylmethyl carbonate. Furthermore, as a lithium salt, thecompound which can be added to an active substance layer of an electrodesuch as Li(CF₃SO₂)₂N, Li(C₂F₅SO₂)₂N, LiPF₆, LiBF₄, LiClO₄, LiAsF₆,LiTaF₆, and LiCF₃SO₃ can be similarly used. The liquid electrolyte mayfurther contain an additive in addition to the components that aredescribed above. Specific examples of the compound include vinylenecarbonate, methylvinylene carbonate, dimethylvinylene carbonate,phenylvinylene carbonate, diphenylvinylene carbonate, ethylvinylenecarbonate, diethylvinylene carbonate, vinylethylene carbonate,1,2-divinylethylene carbonate, 1-methyl-1-vinylethylene carbonate,1-methyl-2-vinylethylene carbonate, 1-ethyl-1-vinylethylene carbonate,1-ethyl-2-vinylethylene carbonate, vinylvinylene carbonate,allylethylene carbonate, vinyloxymethylethylene carbonate,allyloxymethylethylene carbonate, acryloxymethylethylene carbonate,methacryloxymethylethylene carbonate, ethynylethylene carbonate,propargylethylene carbonate, ethynyloxymethylethylene carbonate,propargyloxyethylene carbonate, methylene ethylene carbonate, and1,1-dimethyl-2-methyleneethylene carbonate. Among them, vinylenecarbonate, methylvinylene carbonate, and vinylethylene carbonate arepreferable. Vinylene carbonate and vinylethylene carbonate are morepreferable. Those cyclic carbonate esters may be used either singly orin combination of two or more types.

The gel polymer electrolyte has a constitution that the aforementionedliquid electrolyte is injected to a matrix polymer (host polymer)consisting of an ion conductive polymer. Using a gel polymer electrolyteas an electrolyte is excellent in that the fluidity of an electrolytedisappears and ion conductivity between layers is blocked. Examples ofan ion conductive polymer which is used as a matrix polymer (hostpolymer) include polyethylene oxide (PEO), polypropylene oxide (PPO),polyethylene glycol (PEG), polyacrylronitrile (PAN), polyvinylidenefluoride-hexafluoropropylene (PVdF-HEP), poly(methyl methacrylate (PMMA)and a copolymer thereof.

According to forming of a cross-linked structure, the matrix polymer ofa gel electrolyte can exhibit excellent mechanical strength. For forminga cross-linked structure, it is sufficient to perform a polymerizationtreatment of a polymerizable polymer for forming a polymer electrolyte(for example, PEO and PPO), such as thermal polymerization, UVpolymerization, radiation polymerization, and electron beampolymerization, by using a suitable polymerization initiator.

Furthermore, as a separator, a separator with a heat resistantinsulating layer laminated on a porous substrate (a separator having aheat resistant insulating layer) is preferable. The heat resistantinsulating layer is a ceramic layer containing inorganic particles and abinder. As for the separator having a heat resistant insulating layer,those having high heat resistance, that is, melting point or heatsoftening point of 150° C. or higher, preferably 200° C. or higher, areused. By having a heat resistant insulating layer, internal stress in aseparator which increases under temperature increase is alleviated sothat the effect of inhibiting thermal shrinkage can be obtained. As aresult, an occurrence of a short between electrodes of a battery can beprevented so that a battery configuration not easily allowing aperformance reduction as caused by temperature increase is yielded.Furthermore, by having a heat resistant insulating layer, mechanicalstrength of a separator having a heat resistant insulating layer isimproved so that the separator hardly has a film breaking. Furthermore,because of the effect of inhibiting thermal shrinkage and a high levelof mechanical strength, the separator is hardly curled during theprocess of fabricating a battery.

The inorganic particles in a heat resistant insulating layer contributeto the mechanical strength or the effect of inhibiting thermal shrinkageof a heat resistant insulating layer. The material used as inorganicparticles is not particularly limited. Examples thereof include oxides(SiO₂, Al₂O₃, ZrO₂, TiC₂), hydroxides and nitrides of silicon, aluminum,zirconium and titanium, and a composite thereof. The inorganic particlesmay be derived from mineral resources such as boehmite, zeolite,apatite, kaolin, mullite, spinel, olivine, and mica, or artificiallysynthesized. Furthermore, the inorganic particles may be used eithersingly or in combination of two or more types. From the viewpoint of thecost, it is preferable to use silica (SiO₂) or alumina (Al₂O₃) amongthem. It is more preferable to use alumina (Al₂O₃).

The weight per unit area of heat resistant particles is, although notparticularly limited, preferably 5 to 15 g/m². When it is within thisrange, sufficient ion conductivity is obtained and heat resistantstrength is maintained, and thus desirable.

The binder in a heat resistant insulating layer has a role of adheringinorganic particles or adhering inorganic particles to a porous resinsubstrate layer. With this binder, the heat resistant insulating layeris stably formed and peeling between a porous substrate layer and a heatresistant insulating layer is prevented.

The binder used for a heat resistant insulating layer is notparticularly limited, and examples thereof which can be used include acompound such as carboxymethyl cellulose (CMC), polyacrylronitrile,cellulose, an ethylene-vinyl acetate copolymer, polyvinyl chloride,styrene-butadiene rubber (SBR), isoprene rubber, butadiene rubber,polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE),polyvinyl fluoride (PVF), and methyl acrylate. Among them, carboxymethylcellulose (CMC), methyl acrylate, or polyvinylidene fluoride (PVDF) ispreferably used. Those compounds may be used either singly or incombination of two or more types.

The content of the binder in a heat resistant insulating layer ispreferably 2 to 20% by weight relative to 100% by weight of the heatresistant insulating layer. When the binder content is 2% by weight ormore, the peeling strength between the heat resistant insulating layerand a porous substrate layer can be increased and vibration resistanceof a separator can be enhanced. Meanwhile, when the binder content is20% by weight or less, a gap between inorganic particles is maintainedat an appropriate level so that sufficient lithium ion conductivity canbe ensured.

Regarding the thermal shrinkage rate of a separator having a heatresistant insulating layer, both MD and TD are 10% or less aftermaintaining for 1 hour at conditions of 150° C., 2 gf/cm². By using amaterial with such high heat resistance, shrinkage of a separator can beeffectively prevented even when the internal temperature of a batteryreaches 150° C. due to increased heat generation amount from a positiveelectrode. As a result, an occurrence of a short between electrodes of abattery can be prevented, and thus a battery configuration not easilyallowing performance reduction due to temperature increase is yielded.

[Positive Electrode Current Collecting Plate and Negative ElectrodeCurrent Collecting Plate]

The material for forming the current collecting plate (25, 27) is notparticularly limited, and a known highly conductive material which hasbeen conventionally used for a current collecting plate for a lithiumion secondary battery can be used. Preferred examples of the materialfor forming a current collecting plate include metal materials such asaluminum, copper, titanium, nickel, stainless steel (SUS) and an alloythereof. From the viewpoint of light weightiness, resistance tocorrosion, and high conductivity, aluminum and copper are preferable.Aluminum is particularly preferable. Meanwhile, the same material or adifferent material can be used for the positive electrode currentcollecting plate 27 and the negative electrode current collecting plate25.

[Positive Electrode Lead and Negative Electrode Lead]

Further, although it is not illustrated, the current collector 11 andthe current collecting plate (25, 27) can be electrically connected toeach other via a positive electrode lead or a negative electrode lead.The same material used for a lithium ion secondary battery of a relatedart can be also used as a material for forming a positive electrode leadand a negative electrode lead. Meanwhile, a portion led from an outercasing is preferably coated with a heat resistant and insulatingthermally shrunken tube or the like so that it has no influence on aproduct (for example, an automobile component, in particular, anelectronic device or the like) according to electric leak after contactwith neighboring instruments or wirings.

[Battery Outer Casing Body]

As for the battery outer casing body 29, an envelope-shaped casing tocover a power generating element, in which a laminate film includingaluminum is contained, can be used in addition to a known metal cancasing. As for the laminate film, a laminate film with a three-layerstructure formed by laminating PP, aluminum and nylon in order can beused, but not limited thereto. From the viewpoint of having high outputand excellent cooling performance, and of being suitably usable for abattery for a large instrument such as EV or HEV, a laminate film ispreferable. Furthermore, as the group pressure applied from outside to apower generating element can be easily controlled and thus the thicknessof an electrolyte solution layer can be easily controlled to a desiredvalue, an aluminate laminate is more preferred for an outer casing body.

[Cell Size]

FIG. 4 is a perspective view illustrating the appearance of a flatlithium ion secondary battery as a representative embodiment of asecondary battery. According to a preferred embodiment of the presentinvention, like this secondary battery, a flat stack type laminatebattery having a constitution that the power generating element isenclosed in a battery outer casing body which is formed of a laminatefilm containing aluminum is provided.

As illustrated in FIG. 4, the flat lithium ion secondary battery 50 hasa flat and rectangular shape, and from both sides, the positiveelectrode tab 58 and the negative electrode tab 59 are drawn to extractelectric power. The power generating element 57 is covered by thebattery outer casing material 52 of the lithium ion secondary battery 50with its periphery fused by heat. The power generating element 57 issealed in a state in which the positive electrode tab 58 and thenegative electrode tab 59 are led to the outside. Herein, the powergenerating element 57 corresponds to the power generating element 21 ofthe lithium ion secondary battery 10 illustrated in FIG. 1 as describedabove. In the power generating element 57, plural single battery layers(single cell) 19, which are each formed of the positive electrode(positive electrode active substance layer) 15, the electrolyte layer 17and the negative electrode (negative electrode active substance layer)13, are laminated.

Meanwhile, the lithium ion secondary battery is not limited to a flatshape of laminate type. The winding type lithium ion secondary batterymay have a barrel shape or a flat and rectangular shape obtained bymodifying the barrel shape, and it is not particularly limited. As anouter casing material of the barrel shape, a laminate film can be used,and a barrel can (metal can) of a related art can be used, and thus itis not particularly limited. Preferably, the power generating element isencased with an aluminum laminate film. Weight reduction can be achievedwith such shape.

Furthermore, drawing of the tabs 58 and 59 illustrated in FIG. 4 is notparticularly limited, either. The positive electrode tab 58 and thenegative electrode tab 59 may be drawn from the same side or each of thepositive electrode tab 58 and negative electrode tab 59 may be dividedinto plural tabs and drawn from each side, and thus it is not limited tothe embodiment illustrated in FIG. 4. Furthermore, in a winding typelithium ion battery, it is also possible to forma terminal by using, forexample, a barrel can (metal can) instead of a tab.

A typical electric vehicle has a battery storage space of about 170 L.Since a cell and an auxiliary machine such as a device for controllingcharge and discharge are stored in this space, storage space efficiencyof a cell is about 50% in general. The cell loading efficiency for thisspace is a factor of determining the cruising distance of an electricvehicle. As the size of a single cell decreases, the loading efficiencyis lowered, and thus it becomes impossible to maintain the cruisingdistance.

Thus, in the present invention, the battery structure of which powergenerating element is covered with an outer casing body preferably has alarge size. Specifically, length of short side of a laminate cellbattery is preferably 100 mm or more. Such large-size battery can beused for an automobile. Herein, the length of short side of a laminatecell battery indicates the length of a shortest side. The upper limit ofa length of a short side is, although not particularly limited,generally 400 mm or less.

[Volume Energy Density and Rated Discharge Capacity]

According to the market requirement, a typical electric vehicle needs tohave driving distance (cruising distance) of 100 km or more per singlecharge. Considering such cruising distance, the volume energy density ofa battery is preferably 157 Wh/L or more and the rated capacity ispreferably 20 Wh or more.

Herein, with regard to the non-aqueous electrolyte secondary battery inwhich the positive electrode of this embodiment is used, largeness of abattery is determined in view of a relationship between battery area orbattery capacity, from the viewpoint of a large-sized battery, which isdifferent from a physical size of an electrode. Specifically, thenon-aqueous electrolyte secondary battery of this embodiment is a flatstack type laminate battery, in which the ratio value of a battery area(projected area of a battery including a battery outer casing body) torated capacity is 5 cm²/Ah or more, and the rated capacity is 3 Ah ormore. Only if a battery is prepared to have such high capacity and largearea, a decrease in cycle characteristics is shown as caused by anoccurrence of a local over-charge mode resulting from the aforementioneddeviation in voltage across an electrode plane. On the other hand, in abattery such as an everyday household battery which does not have highcapacity and large area, the deviation in voltage across an electrodeplane is not shown, and thus no decrease in cycle characteristicsresulting from an occurrence of a local over-charge mode is shown (see,Comparative Example 5 which is described below).

Furthermore, the aspect ratio of a rectangular electrode is preferably 1to 3, and more preferably 1 to 2. Meanwhile, the aspect ratio of anelectrode is defined by longitudinal/transversal ratio of a positiveelectrode active substance layer with a rectangular shape. By having theaspect ratio in this range, an advantage of having both the performancesrequired for a vehicle and loading space can be obtained.

[Assembled Battery]

An assembled battery is formed by connecting plural batteries.Specifically, at least two of them are used in series, in parallel, orin series and parallel. According to arrangement in series or parallel,it becomes possible to freely control the capacity and voltage.

It is also possible to form a detachable small-size assembled battery byconnecting plural batteries in series or in parallel. Furthermore, byconnecting again plural detachable small-size assembled batteries inseries or parallel, an assembled battery having high capacity and highoutput, which is suitable for a power source or an auxiliary powersource for operating a vehicle requiring high volume energy density andhigh volume output density, can be formed. The number of the connectedbatteries for fabricating an assembled battery or the number of thestacks of a small-size assembled battery for fabricating an assembledbattery with high capacity can be determined depending on the capacityor output of a battery of a vehicle (electric vehicle) for which thebattery is loaded.

[Vehicle]

The non-aqueous electrolyte secondary battery of the present inventioncan maintain discharge capacity even when it is used for a long periodof time, and thus has good cycle characteristics. It also has highvolume energy density. For use in a vehicle such as an electric vehicle,a hybrid electric vehicle, a fuel cell vehicle, or a hybrid fuel cellvehicle, long service life is required as well as high capacity andlarge size compared to use for an electric and mobile electronic device.As such, the non-aqueous electrolyte secondary battery can be preferablyused as a power source for a vehicle, for example, as a power source foroperating a vehicle or as an auxiliary power source for operating avehicle.

Specifically, the battery or an assembled battery formed by combiningplural batteries can be mounted on a vehicle. According to the presentinvention, a battery with excellent long term reliability, outputcharacteristics, and long service life can be formed, and thus, bymounting this battery, a plug-in hybrid electric vehicle with long EVdriving distance and an electric vehicle with long driving distance percharge can be achieved. That is because, when the battery or anassembled battery formed by combining plural batteries is used for, forexample, a vehicle such as hybrid car, fuel cell car, and electric car(including two-wheel vehicle (motor bike) or three-wheel vehicle inaddition to all four-wheel vehicles (automobile, truck, commercialvehicle such as bus, compact car, or the like)), a vehicle with longservice life and high reliability can be provided. However, the use isnot limited to a vehicle, and it can be applied to various power sourcesof other transportation means, for example, a moving object such as anelectric train, and it can be also used as a power source for loadingsuch as an uninterruptible power source device.

EXAMPLES

The present invention is described in more detail in view of Examplesand Comparative Examples. However, it is evident that the technicalscope of the present invention is not limited to the Examples givenbelow.

(1) Preparation of Lithium Nickel-Based Composite Oxide

To an aqueous solution (1 mol/L) having nickel sulfate, cobalt sulfate,and manganese sulfate dissolved therein, sodium hydroxide and ammoniawere continuously supplied at 60° C. to adjust the pH to 11.3, andaccording to a co-precipitation method, metal composite hydroxide inwhich nickel, manganese, and cobalt were dissolved at molar ratio of50:30:20 was produced.

The metal composite hydroxide and lithium carbonate were weighed suchthat the ratio of the total mole number of metals (Ni, Co and Mn) otherthan Li to the mole number of Li was 1:1, and then thoroughly mixed. Thetemperature was increased at temperature increase rate of 5° C./min,temporary calcination was performed at 900° C. for 2 hours in airatmosphere, the temperature was increased at temperature increase rateof 3° C./min, and then main calcination was performed at 920° C. for 10hours. After cooling to room temperature, an NMC composite oxide(LiNi_(0.50)Mn_(0.30)Co_(0.20)O₂) was obtained as a positive electrodeactive substance. Meanwhile, the average secondary particle diameter(D50(A)) of the obtained NMC composite oxide was 10 μm.

(2) Preparation of Spinel Type Lithium Manganese Composite Oxide

As other positive electrode active substance, a spinel type lithiummanganese composite oxide (LiMn₂O₄) was prepared. Herein, three typeswith different average secondary particle diameter (D50(B)) wereprepared as described below.D50(B)=10 μm, D50(A)/D50(B)=1  LiMn₂O₄(1):D50(B)=15 μm, D50(A)/D50(B)=0.66  LiMn₂O₄(2):D50(B)=5 μm, D50(A)/D50(B)=2  LiMn₂O₄(3):

(3) Production of Positive Electrode

90% by weight in total of any one of the NMC composite oxide which hasbeen prepared in above (1) and the spinel type lithium manganesecomposite oxide which has been prepared in above (2), 5% by weight ofcarbon black as a conductive aid (Super-P, manufactured by 3M Company),5% by weight of polyvinylidene fluoride (PVDF) as a binder (#7200,manufactured by KUREHA CORPORATION), and a suitable amount ofN-methyl-2-pyrrolidone (NMP) as a solvent for controlling slurryviscosity were admixed with one another to prepare a slurry of positiveelectrode active substance. Then, the obtained slurry of positiveelectrode active substance was coated on a surface of an aluminum foil(thickness: 20 μm) as a current collector, dried for 3 minutes at 120°C., subjected to press molding using a roll press machine to produce apositive electrode active substance layer of which planar shape is arectangular shape. The positive electrode active substance layer wasalso formed on the back surface in the same manner as above.Accordingly, a positive electrode obtained by forming a positiveelectrode active substance layer on both surfaces of a positiveelectrode current collector (aluminum foil) was produced. Meanwhile, thecoating amount on a single surface of positive electrode activesubstance layer was 14 mg/cm² (excluding the foil). According to thisprocedure, 16 kinds of positive electrodes with different composition ofa positive electrode active substance were produced as described in thefollowing Table 1 (numbers are present in % by weight).

TABLE 1 Positive electrode active substance Positive NMC elec- compo-Con- trode site LiMn₂O₄ LiMn₂O₄ LiMn₂O₄ ductive symbol oxide (1) (2) (3)aid Binder C1 90 5 5 C2 81 9 5 5 C3 72 18 5 5 C4 63 27 5 5 C5 54 36 5 5C6 45 45 5 5 C7 81 9 5 5 C8 72 18 5 5 C9 63 27 5 5 C10 54 36 5 5 C11 4545 5 5 C12 81 9 5 5 C13 72 18 5 5 C14 63 27 5 5 C15 54 36 5 5 C16 45 455 5

Meanwhile, the size of each positive electrode was any one of □1 to □3which are described in the following Table 2. Herein, L1 and L2described in Table 2 indicate the length of the vertical line and thelength of the horizontal line, respectively, of the flatrectangular-shaped positive electrode active substance layer (with theproviso that, L1≦L2), and D indicates the area of the positive electrodeactive substance layer.

TABLE 2 Aspect ratio L1/mm L2/mm D/cm² L1/L2 □1 100 100 100 1.00 □2 150250 375 1.67 □3 10 8000 800 80.00

(4) Production of Negative Electrode

Subsequently, 95% by weight of artificial graphite as a negativeelectrode active substance, 2% by weight of carbon black as a conductiveaid (Super-P, manufactured by 3M Company), 1% by weight of ammonium saltof carboxy methyl cellulose as a binder, and 2% by weight ofstyrene-butadiene copolymer latex were dispersed in purified water toproduce a slurry of negative electrode active substance. Then, thisslurry of negative electrode active substance was coated on a copperfoil (thickness: 10 μm) to be a negative electrode current collector,dried for 3 minutes at 120° C., subjected to press molding using a rollpress machine to produce a negative electrode. The same treatment wasperformed for the back surface to forma negative electrode activesubstance layer so that a negative electrode having a negative electrodeactive substance layer formed on both surfaces of a negative electrodecurrent collector (copper foil) was produced. Meanwhile, the coatingamount on the negative electrode active substance layer was adjustedsuch that the A/C ratio relative to the opposite positive electrode is1.20 during the production of a test cell described below (accordingly,the coating amount on a single surface of negative electrode activesubstance layer is 6.1 to 7.9 mg/cm² (excluding the foil)).

(5) Production of Test Cell

By alternately laminating, via the separator (thickness: 25 μm, Celgard#2500, manufactured by Polypore K.K.), a positive electrode prepared inabove (3) and the negative electrode prepared in above (4) according toselection as shown in the following Table 3 and selection of theelectrode area from □1 or □2 (three layers of positive electrode andfour layers of negative electrode), a power generating element wasproduced. The obtained power generating element was disposed within abag made of aluminum laminate sheet as an outer casing, and anelectrolyte solution was added thereto. As an electrolyte solution, asolution in which 1.0M LiPF₅ was dissolved in a mixed solvent ofethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio of3:7), in which 1% by mass of vinylene carbonate was added as an additiverelative to 100% by weight of the solution, was used. Herein, the liquidinjection amount of the electrolyte solution was set at an amount whichis 1.40 times of the entire pore volume of the positive electrode activesubstance layer, negative electrode active substance layer, andseparator (the pore volume was obtained by calculation). Subsequently,under vacuum conditions, the opening of an aluminum laminate sheet bagwas sealed such that the tab for taking out current, which had beenconnected to both electrodes, was led to outside, and a test cell as alaminate type lithium ion secondary battery was completed. Accordingly,twenty kinds of test cells which have different kinds and size of apositive electrode were produced as shown in the following Table 3.Meanwhile, the rated capacity (Ah) and the ratio of battery area to therated capacity (cm²/Ah) for the each obtained test cell are shown in thefollowing Table 3.

In addition, the positive electrode prepared in above (3) and thenegative electrode prepared in above (4) are selected as shown in thefollowing Table 3 and, with the electrode area of □3, lamination via aseparator was made as described above. After attaching a tab for takingout the current, it was wound, enclosed in a can as an outer casing, andsealed after injection of an electrolyte solution. Accordingly, twokinds of a test cell with different kinds of a positive electrode (woundtype battery) were produced as shown in the following Table 3(Comparative Examples 6 and 8). Meanwhile, the rated capacity (cellcapacity) (Ah) and the ratio of battery area to the rated capacity(capacity area ratio) (cm²/Ah) for the each obtained test cell are shownin the following Table 3. As described herein, the rated capacity of abattery was obtained as described below.

<<Measurement of Rated Capacity>>

For measurement of rated capacity, a test cell was injected with anelectrolyte solution, allowed to stand for 10 hours or so, and subjectedto initial charge. After that, the measurement was carried out accordingto the following step 1 to 5 at temperature of 25° C., in the voltagerange of 3.0 V to 4.15 V.

Step 1: After constant current charge at 0.2 C to reach 4.15 V, it wasrested for 5 minutes.

Step 2: After Step 1, it was charged for 1.5 hours by constant voltagecharge followed by resting for 5 minutes.

Step 3: After constant current discharge at 0.2 C to reach 3.0 V, it wasdischarged for 2 hours by constant voltage discharge followed by restingfor 10 seconds.

Step 4: After constant current charge at 0.2 C to reach 4.1 V, it wascharged for 2.5 hours by constant voltage charge followed by resting for10 seconds.

Step 5: After constant current discharge at 0.2 C to reach 3.0 V, it wasdischarged for 2 hours by constant voltage discharge followed by restingfor 10 seconds.

Rated capacity: The discharge capacity (CCCV discharge capacity) fromthe constant current discharge to constant voltage discharge of Step 5is used as rated capacity.

(6) Evaluation of Characteristics of Test Cell

The test cell which has been produced in above (5) was allowed to standfor 24 hours, and once the open circuit voltage (OCV) is stabilized,charging was performed at a rate of 1 C up to the cut off voltage of4.25 V. After resting for 1 hour, it was discharged to cut off voltageof 3.0 V.

Meanwhile, the test cell was charged at constant current of 1 C. Then,it was disintegrated in an inert gas atmosphere, and five pointsincluding A, B, C and D at the end and the center part (see, FIG. 5)were punched to have φ10 mm. By using metal lithium as a counterelectrode, the potential was measured. At that time, the differencebetween the maximum potential and the minimum potential among the fivepoints is used as ΔV. The results are shown in the following Table 3.Meanwhile, smaller ΔV indicates better exhibition of the effect of thepresent invention as the over-voltage is promoted in a terminal stage ofcharging of the test cell and the non-uniformity of voltage across anelectrode plane is alleviated.

Furthermore, as a durability test for mimicking the use in anautomobile, charge and discharge cycle test at 1.5 C rate was performedin an incubator at 50° C., which mimics rapid charge, and the capacityretention rate after 300 cycles were calculated. The results are shownin the following Table 3.

TABLE 3 Area Positive electrode Rated capacity Capacity Electrodecapacity ratio ΔV retention Type area (Ah) (cm²/Ah) (V) rate (%)Comparative C1 □2 4.7 81.6 0.35 70 Example 1 Comparative C2 □2 4.5 85.50.26 72 Example 2 Example 1 C3 □2 4.3 89.8 0.13 77 Example 2 C4 □2 4.194.6 0.13 77 Example 3 C5 □2 3.9 99.9 0.11 78 Example 4 C6 □2 3.6 105.80.11 78 Comparative C7 □2 4.5 85.5 0.27 72 Example 3 Example 5 C8 □2 4.389.8 0.12 77 Example 6 C9 □2 4.1 94.6 0.12 77 Example 7 C10 □2 3.9 99.90.11 78 Example 8 C11 □2 3.6 105.8 0.1 78 Comparative C12 □2 4.5 85.50.29 72 Example 4 Example 9 C13 □2 4.3 89.8 0.14 77 Example 10 C14 □24.1 94.6 0.12 78 Example 11 C15 □2 3.9 99.9 0.12 78 Example 12 C16 □23.6 105.8 0.11 78 Comparative C1 □1 1.3 37.4 0.23 79 Example 5Comparative C1 □3 3.4 3.6 0.26 76 Example 6 Comparative C3 □1 1.1 96.20.11 79 Example 7 Comparative C3 □3 3 3.9 0.11 77 Example 8

As shown in the results of Table 3, it was found that, by having theconstitution of the present invention, the test cell with high capacityand large area (□2) has small ΔV and therefore high capacity retentionrate is achieved (cycle durability is improved). It was also found that,when the aspect ratio defined as a longitudinal/transversal ratio of apositive electrode active substance layer is in the range of 1 to 3, theeffect of improving the cycle durability by having the constitution ofthe present invention is fully exhibited. Meanwhile, when □1 (batteryarea of 100 cm²) is used, the effect of improving the cycle durabilityby having the constitution of the present invention is not shown becausethe rated capacity was small per se (it is not a test cell with highcapacity and large area). Similarly, when □3 is used, the effect ofimproving the cycle durability by having the constitution of the presentinvention is extremely small because the area capacity ratio is low(compared to the effect of Comparative Example 8 relative to ComparativeExample 6 in which □3 (aspect ratio of 80.00) is used (capacityretention rate 76%→77%), the effect of Example 1 relative to ComparativeExample 1 in which □2 (aspect ratio of 1.67) is used (capacity retentionrate 70%→77%) is more significant).

The present application is based on Japanese Patent Application No.2013-054106 filed on Mar. 15, 2013, and its disclosure is entirelyincorporated herein by reference.

REFERENCE SIGNS LIST

-   10, 50 Lithium ion secondary battery-   11 Negative electrode current collector-   12 Positive electrode current collector-   13 Negative electrode active substance layer-   15 Positive electrode active substance layer-   17 Separator-   19 Single battery layer-   21, 57 Power generating element-   25 Negative electrode current collecting plate-   27 Positive electrode current collecting plate-   29, 52 Battery outer casing material-   58 Positive electrode tab-   59 Negative electrode tab

The invention claimed is:
 1. A positive electrode for a non-aqueouselectrolyte secondary battery in which a ratio value of a battery areato a rated capacity is 89.8 cm²/Ah or more, the battery area being aprojected area of the non-aqueous electrolyte secondary batteryincluding a battery outer casing body and the rated capacity being 3 Ahor more, the positive electrode comprising: a positive electrode currentcollector; and a positive electrode active substance layer that isformed on a surface of the positive electrode current collector and hasa positive electrode active substance containing a lithium nickel-basedcomposite oxide and a spinel type lithium manganese composite oxide,wherein, when an average secondary particle diameter of the lithiumnickel-based composite oxide is D50(A), a content ratio of the lithiumnickel-based composite oxide in the positive electrode active substancelayer is A [% by mass], the average secondary particle diameter of thespinel type lithium manganese composite oxide is D50(B), and a contentratio of the spinel type lithium manganese composite oxide in thepositive electrode active substance layer is B [% by mass], the positiveelectrode satisfies the following0.5≦D50(A)/D50(B)≦2.0 and0.3≦B/(A+B)≦0.5.
 2. The positive electrode for a non-aqueous electrolytesecondary battery according to claim 1, wherein the lithium nickel-basedcomposite oxide has a composition represented by a general formula:Li_(a)Ni_(b)Mn_(c)Co_(d)M_(x)O₂, wherein a, b, c, d, and x satisfy thefollowing:0.9≦a≦1.2,0≦b≦1,0≦c≦0.5,0≦d≦0.5,0≦x≦0.3,b+c+d=1, and wherein M represents at least one element selected from thegroup consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr.
 3. Thepositive electrode for a non-aqueous electrolyte secondary batteryaccording to claim 2, wherein b, c and d satisfy the followingequations:0.44≦b≦0.51,0.27≦c≦0.31, and0.19≦d≦0.26.
 4. The positive electrode for a non-aqueous electrolytesecondary battery according to claim 1, wherein the positive electrodeactive substance layer has a rectangular shape and an aspect ratio of anelectrode defined as a longitudinal/transversal ratio of arectangular-shaped positive electrode active substance layer is 1 to 3.5. A non-aqueous electrolyte secondary battery comprising: a powergenerating element including a positive electrode, a negative electrodeobtained by forming a negative electrode active substance layer on asurface of a negative electrode current collector, and a separator, thepositive electrode comprising: a positive electrode current collector;and a positive electrode active substance layer that is formed on asurface of the positive electrode current collector and has a positiveelectrode active substance containing a lithium nickel-based compositeoxide and a spinel type lithium manganese composite oxide, wherein aratio value of a battery area to a rated capacity is 89.8 cm²/Ah ormore, the battery area being a projected area of the non-aqueouselectrolyte secondary battery including a battery outer casing body andthe rated capacity being 3 Ah or more, and wherein, when an averagesecondary particle diameter of the lithium nickel-based composite oxideis D50(A), a content ratio of the lithium nickel-based composite oxidein the positive electrode active substance layer is A [% by mass], theaverage secondary particle diameter of the spinel type lithium manganesecomposite oxide is D50(B), and a content ratio of the spinel typelithium manganese composite oxide in the positive electrode activesubstance layer is B [% by mass], the positive electrode satisfies thefollowing:0.5≦D50(A)/D50(B)≦2.0, and0.3≦B/(A+B)≦0.5.
 6. The non-aqueous electrolyte secondary batteryaccording to claim 5, wherein the separator has a heat resistantinsulating layer.
 7. The non-aqueous electrolyte secondary batteryaccording to claim 5, wherein the non-aqueous electrolyte secondarybattery is a flat stack type laminate battery in which the powergenerating element is enclosed in the battery outer casing body which isformed of a laminate film containing aluminum.
 8. The non-aqueouselectrolyte secondary battery according to claim 5, wherein the ratedcapacity is 3 Ah or more.
 9. The non-aqueous electrolyte secondarybattery according to claim 5, wherein the lithium nickel-based compositeoxide has a composition represented by a general formula:Li _(a) Ni _(b) Mn _(c) Co _(d) M _(x) O ₂, wherein a, b, c, d, and xsatisfy the following:0.9≦a≦1.2,0≦b≦1,0≦c≦0.5,0≦d≦0.5,0≦x≦0.3,b+c+d=1, and wherein M represents at least one element selected from thegroup consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr.
 10. Thenon-aqueous electrolyte secondary battery according to claim 5, whereinb, c and d satisfy the following:0.44≦b≦0.51,0.27≦c≦0.31, and0.19≦d≦0.26.
 11. The non-aqueous electrolyte secondary battery accordingto claim 5, wherein the positive electrode active substance layer has arectangular shape and an aspect ratio of an electrode defined as alongitudinal/transversal ratio of a rectangular-shaped positiveelectrode active substance layer is 1 to 3.